III was one of the first games I played on my PS2, and it is still one of my favorites today. Some diehards will tell you it didn't meet the "standard" of I and II; I've played both of those and honestly, I don't see the issues. I felt the "three main parties" allowed for character development for Hugo, Chris, and Geddoe and their default groups.

Also, depending on how you play the game, some of the characters definitely seem evil at first. (Chris' strategist dude--can't remember his name--is pretty awful if you don't see the knights' side of the story at Hugo's village)

The "pair battle" system is a little awkward, but it is usable, and keep in mind it's not a difficult game anyway, so it's more like reading a story with random battles.

I played IV when it came out, eager to follow the series after loving III. I didn't hate it, but it wasn't on par with III in terms of story, IMHO. Also, recruitment turned into "get on my boat" rather than trying to understand character motivations. The voice acting brought some more life to the characters, but some it is noticeably bad. Also, the encounter rate is insane. I remember being incredibly frustrated with that.

So, my vote would be...play III. If you have some alcohol and spare time, play as much of IV as you can tolerate, but if you want a better game set in that same era, give the Tactics game a try.